TDS is an aggregate measurement of all the organic and inorganic material present in a sample of water. This includes dissolved organic compounds, inorganic compounds, salts, minerals, and ions. TDS meters measure the conductivity of the water in parts-per-million (abbreviated as ppm), which is equivalent to measuring the mass of contaminants present per liter of water (abbreviated as mg/L). TDS is a nonselective measurement. It does not differentiate between the road salts dissolved in your well water and the naturally occurring mineral content, like magnesium and sodium. If your TDS levels are above 600, or even in the 1,000s, it is a huge indicator that there is a wildly problematic level of dissolved material present in your water. But if your water’s TDS measures between 300-500, it is considered acceptable and it’s difficult to isolate if any of those dissolved materials are potentially harmful or damaging from a TDS reading alone.
The EPA considers TDS to be a secondary drinking water contaminant. Secondary drinking water contaminants pose no health risks and are though there are suggested optimal levels of these contaminants, the EPA does not enforce these standards. These instead considered to be primarily cosmetic, aesthetic, and technical inconveniences. For example, acidic water is not dangerous to consume but is extremely corrosive and destroys household plumbing. Hard water similarly does not run the risk of making your and your family sick, but it will wreak havoc on your water heaters and household appliances. High levels of iron can turn your water a bright, unattractive orange color, but this doesn’t mean that drinking this water will cause illness.